Drugs? No it's timed to well

Head injury? It would have been noticed at the hospital

That's where Sherlock's theories stopped; his attention was on the nauseous doctor next to him as they rode in the police car to St Bart's

They spent the rest of the day in the lab with Molly, they tested spit, blood, cells, skin, hair and urine of John Watson and came up with nothing, Molly got hold of a friend in the hospital and ordered an MRI but all was well.

Sherlock sat in the high chair at his desk staring at his sleeping friend who had fallen asleep with a few seconds of lying down between two chairs. "I can't lose him" he muttered to himself. More than a statement, it was a confession. He was glad no one but him heard it but felt like he needed to tell John. "I'm an idiot without, inhuman even. I'm… better… with you" he carried on gently, leaning his elbows on his knees so he was closer to John.

It was a couple of hours before John woke up; Sherlock was asleep on the chair opposite him, his coat draped over him.

John's eyes took a minute to adjust in the dark room and he slowly remembered the night before.

His examination results where spread out on the desk Sherlock had claimed for himself; brain scans, blood samples, and every other means of testing where scattered across it along with notes that Sherlock had torn then put back together and torn even smaller out of frustration.

He looked at the sleeping detective, holding back the urge to touch him. The urge he had been trying to stop ever since he saw him in the hospital. To make sure he was real… alive.

John took a deep breath and headed out of the lab. He needed fresh air.

John took to the stairs before he even confessed to himself where he was going. He carried up and out to the roof of St Bart's hospital, cold air hit his face as he stepped out, his cloths and hair where pushed by the wind to one side. John walked across the roof to the edge and looked out onto London, some buildings reflected light off into his eyes, some hid blunt in the wind, invisible as people walked past.

John stood admiring the view for a while before he heard the door slam shut by the wind, making him jump and turn; Sherlock was walking steadily towards him, eyeing the edge of the building. "John…" He called gently, he was standing beside him now, casually checking his vital signs, his eyes, lips, neck, legs where all fine. That's when he noticed his hand shaking under his sleeve, the logical course of action would have been to investigate it, to question it. But he had seen John's hand like that before, when Sherlock was dead.

Instead he snaked his hand around John's, giving it an encouraging squeeze, "I'm here" he said gently making John laugh nervously. "I hate you" John whispered back, "Love you too" Sherlock smiled back, making John shake his head and mutter "Idiot" as they turned from the edge and back inside, as symbiotic 'the past is the past' moments go, John was pretty happy with his.